The present invention generally relates to communication signal processing, and particularly relates to distributed transmit diversity in wireless communication networks.
Maintaining acceptable communication performance in mobile communication environments poses significant challenges. For example, the relative movement between a wireless communication transmitter and receiver gives rise to complex and dynamically changing channel fading conditions. Even in low-mobility circumstances, one or more propagation paths between a particular transmitter and receiver may be severely faded because of obstructions.
Conventional wireless communication networks may employ different forms of transmit diversity to mitigate at least some of the fading problems mentioned above. For example, some types of Code Division Multiple Access (CDMA) networks use simple spatial diversity to improve reception performance under certain conditions. With spatial diversity, the same signal is transmitted from two or more antennas and travels to the intended receiver over different propagation channels. Reception is improved because each propagation channel generally has independent fading characteristics, assuming that the transmit antennas are not co-located elements within closely spaced antenna array.
For co-located transmit antennas, a different form of transmit diversity may be used. It is known, for example, to use space-time coding for the transmission of a given information signal via co-located antenna elements. The use of co-located antenna array elements is a general characteristic of conventional space-time coding systems, wherein different antenna elements in a transmit antenna array are used to transmit space-time coded signals. As one example, the well-known Alamouti scheme generally uses two co-located antenna array elements to transmit a 2×2 space-time code word (STC), which can be decoded by an appropriately configured receiver.